The use of solid, spheroidal catalysts for use in the heterogeneous polymerization of ethylene is well known. The prior art catalysts are typically based on metallocene catalysts or Ziegler-Natta catalysts and are supported on spheroidal magnesium chloride supports. Methods for preparing such catalysts include methods which rely on emulsion, spray drying, and controlled precipitation techniques. These catalysts may provide for improved product morphology and bulk density.
U.S. Pat. Nos. 5,106,804 and 5,439,995 describe the use of a spheroidal catalyst based on a zirconocene single site catalyst supported on spheroidal magnesium chloride particles. Pre-polymerization, followed by polymerization using these catalysts gave polymer with good morphology. The spheroidal magnesium chloride support particles are made in the presence of a non-reactive electron donor compound such as a non-protic ether compound. For further descriptions of spheroidal magnesium chloride particles and their use as supports see CA Pat. Nos. 1,189,053; 2,036,767 and 2,092,769.